The present invention relates to the field of semiconductor wafer preparation. More particularly, the present invention relates to the field of devices that secures semiconductor wafers to work surfaces, such as cutting and dicing machines.
It is ordinary in the art to adhere a semiconductor wafer to tape prior to sawing or cutting the semiconductor wafer into individual die or sub-units. This is done by applying one side of an adhesive tape, such as double-sided sticky tape, to a holder, leaving the remaining side available. The wafer is then placed on the available side of the adhesive tape. The tape, hereinafter referred to as semiconductor wafer tape, secures the individual sub-units in place after cutting and facilitates subsequent handling.
An occurring problem with handling the wafer after the cutting process is sub-unit edge fracture. Wafer sub-unit edge fracture occurs when edges of adjacent wafer sub-units collide. Since these sub-units are extremely thin, the slight force generated by adjacent edge collisions is sufficient to chip or fracture the edges of the sub-units. Edge fracture is primarily due to the redistribution of the wafer weight after cutting. For instance, when the wafer is first placed upon the wafer handling chuck of a wafer handling machine and secured by the wafer tape, the weight is evenly distributed. However, after cutting, the weight of each sub-unit is now distributed only across the area of the tape in contact with the wafer sub-unit. This effect, when applied to each of the sub-units produced by cutting the wafer, causes an overall sagging of the tape across the wafer handling chuck of a wafer handling machine. It is this sagging of the tape that allows the edges of adjacent sub-units to be driven toward each other, frequently resulting in destructive collisions. Therefore, it is desirable to reduce edge fracture or suffer the loss of otherwise viable sub-units.
Ordinarily, to combat sub-unit edge fracture and to otherwise facilitate wafer sub-unit handling, the semiconductor industry uses stretchable wafer tape. Stretchable tapes and methods of using the same are disclosed respectively by Shibata et al. in U.S. Pat. No. 5,316,853 and in U.S. Pat. No. 5,762,744. Moreover, U.S. Pat. No. 5,538,771 issued to Nakayama, et al., also discloses a stretchable semiconductor wafer tape. To use the stretched tapes disclosed in these patents, an uncut semiconductor wafer must first be adhered to the un-stretched wafer tape by any one of a variety of methods.
In one method of applying stretchable wafer tape to a semiconductor wafer, a tape application machine having a tape application diaphragm applies the stretchable semiconductor wafer tape to the back of a semiconductor wafer. In this method, a portion of stretchable semiconductor wafer tape is positioned between a collapsed diaphragm and a of semiconductor wafer. By expanding the machine diaphragm, the stretchable semiconductor wafer tape is brought into contact with the back of the semiconductor wafer, starting at the center of the wafer and gradually moving from the inside of the wafer towards the perimeter of the uncut semiconductor wafer. By gradual application of the stretchable wafer tape from the inside out, the occurrence of air bubbles between the tape and the wafer can be reduced.
Manual methods of applying stretchable wafer tape to the back of semiconductor wafers also exist. For instance, one method uses ring devices that snap together with portion stretchable wafer tape between the ring devices. The action of snapping the rings together over the stretchable semiconductor wafer tape pulls the wafer tape flat before attachment of the semiconductor wafer. Another method of applying stretchable semiconductor wafer tape involves manual application of the wafer tape to the backside of a semiconductor wafer. In this method, a person brushes or wipes the wafer tape onto the backside of the semiconductor wafer using outwardly concentric motions. As it was in the case of the tape application machine discussed above, the goal of both of these manual methods is also to reduce the likelihood of bubbles being trapped between the stretchable wafer tape and the semiconductor wafer.
After the stretchable wafer tape is applied to the uncut semiconductor wafer, the uncut wafer is cut into multiple sub-units leaving the film of the stretchable tape generally intact. Thereafter, placing a tension across the stretchable tape expands the tape and separates the edges of adjacent sub-units. Thereafter, a die-picking machine is used to handle the physically separated individual sub-units. In use, stretchable wafer tape reduces edge fracture of adjacent sub-units by pulling apart, or stretching horizontally, the tape to which the sub-units are adhered.
One shortfall of using the stretchable tape disclosed is the step required for stretching these wafer tapes. Generally, a tensile force must be applied to the stretchable tape to cause the tape to stretch. The equipment required to apply the tensile force can be expensive or difficult to set up. Moreover, the manufacture of stretchable tape can be fairly complex and accordingly expensive. Therefore, there is a need for a device, such as a new semiconductor wafer diaphragm, that is inexpensive but solves the problem of sub-unit edge fracture. The present invention promotes the reduction of sub-unit edge fracture in an inexpensive manner and permits the continued use of ordinary semiconductor wafer handling equipment.
It is an object of the present invention to reduce semiconductor die or sub-unit edge fracture using a semiconductor wafer diaphragm.
It is a further object of the present invention to reduce semiconductor die or sub-unit edge fracture using a semiconductor wafer diaphragm and ordinary semiconductor wafer handling equipment.